Matrix driver

ABSTRACT

A matrix driver is provided, comprising a plurality of light emitting diodes, energizing means for successively pulse-driving and scanning the light emitting diodes, and control means for instructing the energizing means about the sequence of scanning, characterized by protective means for preventing one specified diode among the light emitting diodes from being continuously pulse-energized.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an optical coordinate input device and, moreparticularly, to a matrix driver for scanning, driving, and controllingindividual diodes contained in a diode matrix composed of a plurality oflight emitting diodes.

2. Description of the Prior Art

The optical coordinate input device comprises, for example, a lightemitting element array. This array includes a plurality of lightemitting diodes arranged in the form of a matrix wherein each lightemitting diode is driven and caused to emit light when a row signal anda column signal pertinent thereto, serving as scanning signals, coincidein timing with each other. The light emitting diodes are driven bypulses, and the peak value of a current supplied to each diode duringthe scanning is made as large as some ten times the rated value duringthe static driving.

Examples of the foregoing type of optical coordinate input device aredisclosed in U.S. Pat. Nos. 3,764,813; 3,775,560; and 3,860,754.

According to these patents, the row signals and the column signals aregiven each in the form of a pulse signal of square waveform. Therefore,if some malfunction occurs in a section for generating such pulsesignals and a "high" level is preserved, only light emitting diodeslocated at row-column positions pertinent to the pulse signals kept atthat level are caused to emit light continuously. As a result, thediodes would be destroyed due to continued energization, or the lifetimewould be shortened.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a matrix driver forlight emitting diodes which prevents continued energization of anypeculiar light emitting diodes even when a signal state designatingthese diodes becomes abnormal.

To achieve the foregoing object, the present invention provides a matrixdriver comprising a plurality of light emitting diodes, energizing meansfor successively pulse-driving and scanning the light emitting diodes,and control means for instructing the energizing means about thesequence of scanning, which is characterized by protective means forpreventing one specified diode among the light emitting diodes frombeing continuously pulse-energized.

In another feature, the present invention provides a matrix drivercomprising a diode matrix composed of a plurality of light emittingdiodes arranged in the form of a matrix, scanning means for providingscanning signals to scan the plurality of light emitting diodes, drivingmeans for driving and causing the designated light emitting diodes toemit light in accordance with the scanning signals, and driveterminating means for supplying a drive terminating signal to thedriving means when the scanning signals come to a standstill. The driveterminating means may be a monostable multivibrator.

In still another feature, the present invention provides a matrix drivercomprising a diode matrix composed of a plurality of light emittingdiodes, signal supplying means for supplying a plurality of row signalsand column signals, driving means for driving the light emitting diodeswithin the diode matrix designated by the row signals and the columnsignals, and drive control means for controlling the driving means sothat when the row signals and the column signals become unchanged aposition devoid of any light emitting diodes is designated. The matrixdriver may include capacitive coupling means for supplying the rowsignals and the column signals to the driving means. Further, the drivecontrol means may be monostable multivibrator circuits being actuated bythe respective row signals and column signals.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a first embodiment of a matrixdriver according to the present invention;

FIGS. 2 and 3 are circuit diagrams showing second and third embodiments,respectively, of the present invention;

FIG. 4 is a diagram showing an example of a resetequipped multivibrator;and

FIG. 5 is a circuit diagram showing a fourth embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described in detailwith reference to the drawings.

FIG. 1 shows a first embodiment of a matrix driver according to thepresent invention. The illustrated matrix driver includes a diode matrixcomposed of light emitting diodes D, having m rows and n columns. Thatis, (m×n) light emitting diodes are arranged in the form of a matrix,indicated by D₁₁ -D_(1n), D₂₁ -D_(2n), . . . , D_(m1) -_(mn).

Signals for driving and controlling these light emitting diodes D aresupplied through a CPU 10. Specifically, a plurality of row controlsignals Sl₁ -Sl_(p) are provided form row signal output terminals Ol₁-Ol_(p) of the CPU 10, and a plurality of column control signals Sr₁-Sr_(q) are provided from column signal output terminals Or₁ -Or_(q) ofthe CPU 10. These row control signals Sl₁ -Sl_(p) are supplied tocorresponding signal input terminals I₁ -I_(p) of a row address decoder20. The column control signals Sr₁ -Sr_(q) are supplied to correspondingsignal input terminals I₁ -I_(q) of a column address decoder 30.

Signal output terminals O₁ -O_(m) of the row address decoder 20 areconnected through PNP transistors T₁ -T_(m) to the corresponding basesof m PNP transistors Ql₁ -Ql_(m) for driving the row side of the diodematrix and provide row signals SL₁ -SL_(m) serving as scanning signals.The bases of the transistors T₁ -T_(m) are connected in common andgrounded.

Similarly, signal output terminals O₁ -O_(n) of the column addressdecoder 30 are connected through PNP transistors T'₁ -T'_(n) to thecorresponding bases of n NPN transistors Qr₁ -Qr_(n) for driving thecolumn side of the diode matrix and provide column signals SR₁ -SR_(n).The bases of the transistors T'₁ -T'_(n) are connected in common with aQ terminal of a re-triggerable monostable multivibrator 40. As thisre-triggerable monostable multivibrator 40 an integrated circuit"HD74LS123" is used in the embodiment which has A and B inputs and aClear input. The A input is fixed to "L" and the B input is fixed to"H", and the Clear input is connected to a control terminal CON of theCPU 10. With the A and B inputs of the retriggerable monostablemultivibrator 40 being fixed as described above, an "L" pulse signal isprovided from the Q terminal when an "H" pulse signal is applied to theClear input, whereas the level of the Q terminal transfers to "H" whenan "L" pulse signal is applied to the Clear input. On the other hand, ifthe Clear input is held at "L" or "H", the Q terminal is kept in the "H"state.

The emitters of the transistors Ql₁ -Ql_(m) are connected in common witha driving voltage source +Vcc, and the collector of each transistor isconnected in common with the anodes of the light emitting diodes of thecorresponding row. The emitters of the transistors Qr₁ -Qr_(n) areconnected in common and grounded, and the collector of each transistoris connected through a resistor, R₁ -R_(n), in common to the cathodes ofthe light emitting diodes of the corresponding column.

The operation of the matrix driver of the foregoing configurationaccording to the present invention will now be described.

The CPU 10 receives a pulse signal of a certain period from a pulseoscillator not shown and provides the row control signals Sl₁ -Sl_(p)and the column control signals Sr₁ -Sr_(q) so that in response to thesecontrol signals the individual light emitting diodes located at desiredrowcolumn positions within the diode matrix are successively caused toemit light one at a time. These control signals Sl₁ -Sl_(p) and Sr₁-Sr_(q) are of the square waveform type.

Consider now the case of causing one diode D₂₂, for example, to emitlight. This diode D₂₂ is positioned at the spot of 2nd row and 2ndcolumn, so the row address must be "2" and the column address must be"2".

During the operation, the CPU 10 provides the row control signal Sl₂ andthe column control signal Sr₂. Consequently, the signal input terminalsI_(p), . . . , I₂, I₁ of the row address decoder 20 are supplied withaddress signals "O, . . . , 1, O"; thus, the row address decoder 20decodes these address signals as "2" and provides the row signal SL₂serving as the scanning signal from the signal output terminal O₂.Similarly, since the signal input terminals I_(q), . . . , I₂, I₁ of thecolumn address decoder 30 are supplied with address signals "O, . . . ,1, O", the column address decoder 30 decodes these address signals as"2"0 and provides the column signal SR₂ serving as the scanning signalfrom the signal output terminal O₂.

However, during the non-scanning interval, the signal output terminalsO₁ -O_(m) of the row address decoder 20 are held at "H", and theforegoing row signal SL₂ of 2nd row is now given in the form of an "L"signal. Therefore, the collector of the transistor T₂ is changed to "L"and it is turned on; thus, the base voltage of the driving transistorQl₂ of 2nd row is changed to "L". Similarly, during the non-scanninginterval, the signal output terminals O₁ -O_(n) of the column addressdecoder 30 are held at "L", and the foregoing column signal SR₂ of 2ndcolumn is now given in the form of an "H" signal. On the other hand, theCPU 10 provides a pulse signal P of "H" level from its control terminalCON each time it provides the column signal, and this pulse signal P issupplied to the Clear input of the re-triggerable monostablemultivibrator 40; thus, the Q terminal is changed to "L". As a result,the bases of the transistors T'₁ -T'_(n) are changed to "L".Consequently, the emitter of the transistor T'₂ is changed to "H" owingto the column signal SR₂ and it is turned on, then the base voltage ofthe driving transistor Qr₂ of 2nd column is changed to "H". Accordingly,there is formed a closed circuit passing through the positive voltagesource +Vcc, the emitter-collector of the tansistor Ql₂, the diode D₂₂,the resistor R₂, the collector-emitter of the transistor Qr₂ , and theground, so that only one light emitting diode D₂₂ is energized to emitlight.

The foregoing relates to the control operation for causing the diode D₂₂to emit light. In the same way as the above, other diodes of the matrixcan be controlled individually so as to emit light by the row controlsignals Sl₁ -Sl_(p) and the column control signals Sr₁ -Sr_(q) providedfor the CPU 10.

During the operation, if either the pulse oscillator or the CPU 10 hasbecome abnormal, the row signal Sl₂ and the column signal Sr₂, forexample, are fixed to either "L" or "H". In such a case, the transistorQl₂ of 2nd row and the transistor Qr₂ of 2nd column tend to be held inthe conducting state to thereby cause the diode D₂₂ to emit lightcontinuously.

In this embodiment, however, the Clear input of the re-triggerablemonostable multivibrator 40 is connected with the control terminal CONof the CPU 10. Therefore, when either the pulse oscillator or the CPU 10has become abnormal, the control terminal CON of the CPU 10 is fixed toeither "L" or "H", as a result, the Clear input of the re-triggerablemonostable multivibrator 40 is held at "L" or "H" and its Q terminal ismaintained in the "H" state. Consequently, the transistors T'₁ -T'_(n)become the non-conducting state and all the driving transistors Qr₁-Qr_(n) become the non-conducting state too. Accordingly, the otherlight emitting diodes D, as well as the light emitting diode D₂₂, cannotbe energized and are prevented from becoming destroyed.

FIG. 2 shows a second embodiment of the present invention. In thisembodiment, a counter 1 and a counter 2 of the CPU 10 count a pulsesignal given from the pulse oscillator not shown and providedindividually the row control signals Sl₁ -Sl_(p) and the column controlsignals Sr₁ -Sr_(q) each time of counting. A counter 3 of the CPU 10provides a negative pulse signals P' each time a certain number of clockpulses are supplied from a clock circuit 10a. This negative pulse signalP' is applied through a condenser Ct and a resistor Rt to the bases ofthe transistors T'₁ -T'_(n). The time constant of these condenser Ct andresistor Rt is set equal to or larger than the period of the pulsesignal P'. The bases of the transistors T'₁ -T'_(n) are applied throughthe resistor Rt with the source voltage +Vcc. For reference, the clockcircuit 10a is used also as a means for synchronizing the respectivecounters.

Normally, in this embodiment, each time the row signals SL₁ -SL_(n) andthe column signals Sr₁ -SR_(n) are provided from the row address decoder20 and the column address decoder 30, the pulse signal P' is providedfrom the counter 3 of the CPU 10, and this pulse signal P' turns on thetransistors T'₁ -T'_(n) ; thus, the light emitting diodes D are scannedsuccessively to emit light.

During the operation, if either the pulse oscillator or the CPU 10 hasbecome abnormal, the counter 3 of the CPU 10 is fixed to "L" or "H" andthe source voltage +Vcc is continuously applied through the resistor Rtto the bases of the transistors T'₁ -T'_(n). Consequently, thetransistors T'₁ -T'_(n) are made non-conductive, and thus, energizationof all the light emitting diodes D is terminated in a similar manner tothe foregoing.

FIG. 3 shows a third embodiment of the present invention. In thisembodiment, there are interposed reset-equipped one-shot multivibrators50 between the signal output terminals O₁ -O_(m) of the row addressdecoder 20 and the driving PNP transistors Ql₁ -Ql_(m). Further,reset-equipped one-shot multivibrators 50' are interposed between thesignal output terminals O₁ -O_(n) of the column address decoder 30 andthe driving NPN transistors Qr₁ -Qr_(n). The multivibrator 50 has, asshown in FIG. 4, a reset input to be connected with each signal outputterminal of the row address decoder 20, and a Q terminal to be connectedwith the base of each PNP transistor, Ql₁ -Ql_(m). The time constant ofa condenser Ct' and a resistor Rt' is set so that a negative pulse isprovided from the Q terminal whose pulse duration is equal to or largerthan that of the row signal. This reset-equipped multivibrator 50provides a negative pulse from its Q terminal each time a negative pulseis applied to the reset input. Accordingly, when some row signal, forexample, the row signal SL₂, of "L" level is provided from the rowaddress decoder 20, a negative pulse is provided from the Q terminal ofthe corresponding resetequipped multivibrator 50 and the PNP transistorQl₂ is turned on.

Similarly, the other reset-equipped multivibrator 50' has a reset inputto be connected with each signal output terminal of the column addressdecoder 30 and a Q terminal to be connected with the base of each NPNtransistor, QR₁ -QR_(n), whose time constant on the output side is setin a similar manner to the above. This reset-equipped multivibrator 50'provides a positive pulse from its Q terminal each time a positive pulseis applied to the reset input. Accordingly, if, for example, the columnsignal SR₂ of "H" level is provided form the column address decoder 30,a positive pulse is provided from the Q terminal of the correspondingreset-equipped multivibrator 50' and the NPN transistor QR₂ is turnedon. As a result, the light emitting diode D₂₂ is driven to emit light.

If either the pulse oscillator or the CPU 10 has become abnormal, therow signals SL₁ -SL_(m) and the column signal Sr₁ -SR_(n) come to astandstill; thus, all the Q terminals of the reset-equippedmultivibrators 50 are held at "H" level, whereas all the Q terminals ofthe reset-equipped multivibrators 50' are held at "L" level.Accordingly, the driving transistors Ql₁ -Ql_(m) and Qr₁ -Qr_(n) aremaintained in the non-conducting state, and energization of all thediodes D is terminated.

For reference, in the embodiment shown in FIG. 3, the same effect can beattained by the use only of either group of reset-equippedmultivibrators 50 or 50'.

FIG. 5 shows a fourth embodiment of the present invention. In thisdrawing, the diode matrix comprises m rows and n columns and includes(m×n-1) light emitting diodes. Specifically, these light emitting diodesdistributed are indicated by D₁₁ -D_(1n), D₂₁ -D_(2n), D₃₁ -D_(3n), . .. , D_(ml) -D_(m)(n- 1), and the position of D_(mn) has no lightemitting diode.

Signals for driving and controlling these light emitting diodes D aresupplied through the CPU 10. Specifically, a plurality of row controlsignals Sl₁ -Sl_(p) are provided from the row signal output terminalsOl₁ -Ol_(p), and another plurality of column control signals Sr₁ -Sr_(q)are provided from the column signal output terminals Or₁ -Or_(q).

These row control signals Sl₁ -Sl_(p) are supplied through a pluralityof condensers Cl₁ -Cl_(p) to the signal input terminals I₁ -I_(p) of therow address decoder 20, and the column control signals Sr₁ -Sr_(g) aresupplied through a plurality of condensers Cr₁ -Cr_(g) to the signalinput terminals I₁ -I_(q) of the column address decoder 30. The inputterminals I₁ -I_(p) of the row address decoder 20 are grounded throughresistors Rl₁ -Rl_(p), and the input terminals I₁ -I_(q) of the columnaddress decoder 30 are grounded through resistors Rr₁ -Rr_(q).

The signal output terminals O₁ -O_(m) of the row address decoder 20 areconnected to the bases of m PNP transistors Ql₁ -Ql_(m) for driving therow side of the diode matrix, thus supply the row signals SL₁ -SL_(m)thereto.

Similarly, the signal output terminals O₁ -O_(n) of the column addressdecoder 30 are connected to the bases of n NPN transistors Qr₁ -Qr_(n)for driving the column side of the diode matrix, thus supply the columnsignals Sr₁ -SR_(n) thereto.

The emitters of the transistors Ql₁ -Ql_(m) are connected in common withthe driving voltage source +Vcc, and each collector is connected incommon with the anodes of light emitting diodes of the correspondingrow.

Similarly, the emitters of the transistors Qr₁ -Qr_(n) are grounded incommon, and each collector is connected through a resistor, R₁ -R_(n),to the cathodes of light emitting diodes of the corresponding column incommon.

The row address decoder 20 operates in such a manner that when a givenrow control signal is applied as the address signal it provides the rowsignals SL_(m) from the signal output terminal O_(m), and if no addresssignal is applied it also provides the row signal SL_(m) from the signaloutput terminal O_(n). Similarly, the column address decoder 30 operatesin such a manner that when a given column control signal is applied asthe address signal it provides the column signal SR_(n) from the signaloutput terminal O_(n), and if no address signal is applied it alsoprovides the column signal SR_(n) from the signal output terminal O_(n).

The operation of the foregoing configuration will now be described.

The CPU 10 receives a pulse signal of a certain period from the pulseoscillator not shown and provides the row control signals Sl₁ -Sl_(p)and the column control signals Sr₁ -Sr_(g) so that in response to thesecontrol signals the individual light emitting diodes located at desiredrow-column positions within the diode matrix are successively caused toemit light one at a time. These control signals Sl₁ -Sl_(p) and Sr₁-Sr_(g) are of the square waveform type.

Consider now the case of causing one diode D₂₂, for example, to emitlight. This diode D₂₂ is positioned at the spot of 2nd row and 2ndcolumn, so the row address must be "2" and the column address must be"2".

During the operation, the CPU 10 provides the row control signal Sl₂ andthe column signal Sr₂. Consequently, the signal input terminals I_(p), .. . , I₂, I₁ of the row address decoder 20 are supplied with addresssignals "O, . . . , 1, O"; thus, the row address decoder 20 decodesthese address signals as "2" and provides the row signal SL₂ from thesignal output terminal O₂. Similarly, since the signal input terminalsI_(q), . . . , I₂, I₁ of the column address decoder 30 are supplied withaddress signals "O, . . . , 1, O", the column address decoder 30 decodesthese address signals as "2" and provides the column signal SR₂ from thesignal output terminal O₂.

However, during the non-scanning interval, the signal output terminalsO₁ -O_(m) of the row address decoder 20 are held at "H", and theforegoing row signal SL₂ of 2nd row is now given in the form of an "L"signal. Therefore, the base voltage of the driving transistor Ql₂ of 2ndrow is changed to "L". Similarly, during the non-scanning interval, thesignal output terminals O₁ -O_(n) of the column address decoder 30 areheld at "L", and the foregoing column signal SR₂ of 2nd column is nowgiven in the form of an "H" signal. Therefore, the base voltage of thedriving transistor Qr₂ of 2nd column is changed to "H". Accordingly,there is formed a closed circuit passing through the positive voltagesource +Vcc, the emittercollector collector of the transistor Ql₂, thediode D₂₂, the resistor R₂, the collector-emitter of the transistor Qr₂,and the ground, so that the two transistors Ql₂ and Qr₂ are turned onand only the diode D₂₂ is energized to emit light.

The foregoing relates to the control operation for causing the diode D₂₂to emit light. In the same way as the above, other diodes of the matrixcan be controlled individually so as to emit light by the row controlsignals Sl₁ -Sl_(p) and the column control signals Sr₁ -Sr_(q) providedfrom the CPU 10.

During the operation, if either the pulse oscillator or the CPU 10 hasbecome abnormal, the row signal Sl₂ and the column signal Sr₂, forexample, are fixed to either "L" or "H". In such a case, if thecondensers Cl₂ and Cr₂ were not included, the row address decoder 20 andthe column address decoder 30 are held in the foregoing abnormal state.As a result, the transistor Ql₂ of 2nd row and the transistor Qr₂ of 2ndcolumn are held in the conducting state, so that the diode D₂₂ emitslight continuously.

On the contrary, in this embodiment, the row control signals Sl₁ -Sl_(p)and the column control signals Sr₁ -Sr_(q) are supplied through therespective condensers to the decoders 20 and 30, respectively.Therefore, in the foregoing abnormal state, the row signal Sl₂ and thecolumn signal Sr₂ are prevented from reaching the subsequent stages byboth condensers Cl₂ and Cr₂. Specifically, two voltages to be applied tothe individual signal input terminals I₂ of the two decoders 20 and 30are varied by the time constant of the resistor Rl₂ and the condenserCl₂ and the time constant of the resistor Rr₂ and the condenser Cr₂. Or,in accordance with these time constants the row control signal Rl₂ andthe column control signal Rr₂ are changed smoothly from "H" to "L".Consequently, any part of the address signal does not become supplied tothe row address decoder 20 and the column address decoder 30. As aresult, the row signal SL_(m) is provided from the signal outputterminal O_(m) of the row address decoder 20 and the column signalSR_(n) is provided from the signal output terminal O_(n) of the columnaddress decoder 30, and the driving transistors Ql_(m) and Qr_(n) areturned on. Accordingly, at the abnormal time, the position of D_(mn)within the diode matrix is surely scanned and since this position has nolight emitting diode arranged there, destruction of any light emittingdiode can surely be prevented.

Although the row control signals Sl₁ -Sl_(p) and the column controlsignals Sr₁ -Sr_(q) are supplied through the capacitive elements toeither the address decoder 20 or 30, these elements may be replaced withmonostable multivibrators. In the latter case, in response to the risingof each control signal each pulse signal of a certain duration isapplied to the input terminal, I₁ -I_(p), I₁ -I_(q), of the decoder, 20,30. Therefore, even if some control signal maintains its outputtingstate, no influence results after generation of one pulse; thus, it ispossible to scan successively the D_(mn) position having no lightemitting diode, similarly to the other positions.

In this embodiment, it is also possible to define external row-columnpositions not included in the diode matrix. If so modified, when the rowand column control signals are prevented from changing, therebyresulting in the abnormal state, these external row-column positions aredesignated by the two decoders 20 and 30.

According to the present invention, since the driving means for causingthe light emitting diodes to emit light are deactivated when thescanning signals come to a standstill, the continued emission action ofthe light emitting diodes that would otherwise be caused owing to, forexample, a trouble of the device can surely be prevented. Thus, therecan be provided the matrix driver capable of causing the light emittingdiodes to emit light stably over a long time.

Further, since the position where no light emitting diode exists isautomatically designated when the signals for controlling the row andcolumn have become abnormal, a peculiar light emitting diode can beprevented from emitting light continuously. Thus, there can be providedthe matrix driver which does not destroy any diodes and shorten thelifetime.

I claim:
 1. A matrix driver comprising:a diode matrix composed of aplurality of light emitting diodes arranged in the form of a matrix;scanning means for providing scanning signals to scan said plurality oflight emitting diodes; driving means for driving and causing therespective light emitting diodes to emit light in accordance with saidscanning signals; and drive terminating means for supplying a driveterminating signal to said driving means when said scanning signals cometo a standstill, wherein said drive terminating means is a monostablemultivibrator having an input terminal connected to said scanning meanswhich detects when said scanning signals come to a standstill and anoutput terminal connected to said driving means for providing said driveterminating signal thereto.
 2. A matrix driver according to claim 1,wherein said driving means includes a plurality of row driving elements,each of which is connected to one end of each of the light emittingdiodes in a corresponding row, and a plurality of column drivingelements, each of which is connected to another end of each of the lightemitting diodes in a corresponding column, and wherein one of saidplurality of row driving elements and plurality of column drivingelements have respective base terminals thereof connected to said outputterminal of said monostable multivibrator for shutting off saidplurality of driving elements when the standstill state of the scanningsignals is detected.